Out of genuine curiosity, if we are to think about it, I would like to ask: if all these people are using their shoulders in connection with their other skills, and this is to be taken as detrimental, then is that because they have determined an actual use or benefit to that in spite of this claim, or does this actually detract from their skills? I'd just like to understand why/how this is limiting their displayed ability, before we take it as a given.

I have never seen the benefit. Most of those who talk about it end up one-side weighted and on the floor, or easily blocked and blown through...dang...there's that martial talk again!

The use of the shoulder is going to isolate the arm from a clean path of power through the body.
There are other more sophisticated things you can do in generating power in the hand from the hara/ground...say in one direction, while the elbow can generate a different force in an entirely different direction... and so on. There are various ways the hand itself can express power from different parts of the body. Some of that joins IP to IS and aiki.
None of that is going to work when the arm/shoulder is in isolation.
Cheers
Dan